Bigger, scarier weapons help jumping spiders woo girls

Red-headed guys with bulging eyes and a unibrow have a greater chance of winning the girl – such is the case at least for jumping spiders.

In fact, the bigger a male jumping spider’s weapons appear to be, the more likely his rival will slink away without a fight, leaving the bigger guy a clear path to the waiting female.

Duke University graduate student Cynthia Tedore, working with her dissertation advisor, visual ecologist Sonke Johnsen, wanted to know what visual signals matter most to magnolia green jumping spiders, which have an impressive array of eyes, including two giant green ones that face forward.

Vision is clearly important to these quarter-inch animals, which can be “very predaceous and aggressive,” when love is in the air.

Tedore’s lab in the basement of Duke’s biological sciences building is lined with wire shelves covered with row after row of Lucite boxes, each holding an individual chartreuse jumping spider.

In pairs, 24 males squared off for 10 minutes in “the arena,” a box festooned with female silk to put the males in a fighting frame of mind.

Over the course of 68 of these cage matches, the male with the bigger chelicerae, heavy, bristling fangs hanging in front of their mouth parts, usually scared the other guy off without a fight.

“The males wave their forelegs at each other for a period, and then the smaller male runs off,” Tedore said.

“That’s why we think they’re using vision to size each other up. Most of the time, the smaller one will run away before it comes to blows,” he explained.